The present invention relates to a wideband power adder-divider for high-frequency circuits of a planar structure and produced more specifically in accordance with printed circuit techniques in microstrip form. The invention also relates to an impedance transformer based on this adder-divider.
The solution which is most frequently employed for impedance matching purposes is the use of quarterwave transformers, particularly as described in the article "General Synthesis of Quarter-Wave Impedance Transformers," H. J. Riblet, IRE Trans. MTT, January 1957, pages 36 to 43, or in the article "Design of stepped microstrip components", G. Kompa, The Radio and Electronic Engineer, Vol. 48, No. 1/2, January/February 1978, pages 53-63 (particularly FIG. 13). These transformers, however, only match impedances for one single frequency. The reflections which are produced in the region of the two discontinuities do not counterbalance each other outside a band of approximately 1 octave centred at this frequency.
A better solution is the use of a transmission line having a non-uniform width ("taper") which is equivalent to an impedance transformer formed by a larger number of gaps of small dimensions. Such a transmission line is described in the article "Impedance Matching by Tapered Transmission Lines", A. H. Hall, The Microwave Journal, March 1966, pages 109 to 114. With such an arrangement a much beter passband and a much better, perhaps even optimum, distribution of the local reflections are obtained, but at the expense of a longer total length.